Recent family studies of microsatellite markers in multiplex families with ankylosing spondylitis (AS) have identified other regions on other chromosomes that, in addition to genes of the major histocompatibility complex such as HLA-B27, heighten the risk for AS. Four hundred (400) families with two affected sibs with AS plus their parents and unaffected siblings will have 50 cc of blood drawn and clinical features of their disease inquired by questionnaire and by review of medical records. Subjects and siblings who answer yes to questionnaire for back pain and those with diagnosis of AS will be examined spinal mobility. Genomic DNA will be abstracted from the whole blood and HLA-B27 typing done by DNA analysis. The DNA will also be used for microsatellite analysis of candidate genes. The results of these studies will be pooled with those from ongoing studies in England and France to determine the genes responsible for AS.